SC17 - alkali Metals Flashcards
What are the properties of lithium ?
Lithium has the electron structure (2,1).
Lithium is the least reactive of the alkali metals.
Lithium burns with a crimson flame when it reacts with oxygen.
Lithium floats on the surface of water and will release bubbles of hydrogen gas (it effervesces)
What are the properties of sodium ?
Seneca
Sodium has the electron structure (2,8,1).
Sodium is more reactive than lithium because its outer electron is less strongly attracted to the positively charged nucleus. This is because it is a greater distance from the positive charge of the atom’s nucleus.
The metal floats on the surface of water, which releases enough heat to melt the sodium. The sodium moves quickly across the surface of the water.
Sodium burns with a yellow/orange flame when it reacts with oxygen.
What are the properties of potassium ?
Seneca
Potassium has the electron structure (2,8,8,1).Potassium is more reactive than lithium and sodium because its outer electron is least strongly attracted to the nucleus.The metal floats on the surface of water, and has a similar, but more vigorous, reaction compared with sodium.Potassium burns with a lilac flame when it reacts with oxygen.
Trend in group 1 and 2
Seneca
All group 1 (and group 2) elements end withium.
Alkali metals reactions with chlorine
Seneca
A metal chloride is formed (e.g. sodium chloride), which dissolves in water to give a colourless solution.
Alkali metals reaction with oxygen
Rapidly turns from silvery shiny to dull as a metal oxide (e.g. potassium oxide) is produced.
Alkali metals reaction with water
Seneca
The metal floats on the surface and melts to create a metal hydroxide (e.g. lithium hydroxide).When they react with water, the energy released is enough to melt the metal.
Reactions of reactive metals with water
Potassium, sodium and lithium all react quickly with cold water to produce a metal hydroxide and hydrogen gas.
Potassium reaction with water
Potassium is the most reactive so reacts very quickly.The hydrogen produced ignites instantly and the metal also sets alight, sparking and burning with a lilac flame.
Sodium reaction with water
Sodium fizzes rapidly and melts to form a ball that moves around on the water surface.
Lithium reaction with water
Lithium fizzes steadily and floats, becoming smaller until reaction complete, unvisible.
Electron shells affect on reactivity
there are more electron shells in between the nucleus and outer electron, which shields the electron from the nuclear charge.This means that the electron is more easily lost, so the atom is more reactive.
Halogen properties
Elements in group 7 in the periodic table are called halogens. They have 7 electrons in their outer shell. They are very reactive because they easily accept an electron into this outer shell. They have similar properties and react in similar ways.
Salts of a halogen properties
When a metal atom transfers its outer electron to a non-metal atom (like a group 7 atom), salts are formed.The result is a compound where all the ions have a full outer shell.
Reactivity trends in halogens
Reactivity
As you go down the group, the halogens become less reactive. This is because:The atoms gain more electron shells.The outer electron shell is further from the nucleus.The attraction between the nucleus and the electron (to be gained from another element) decreases.
How are halogens presented (something to remember)
In their elemental form, halogens share electrons to make diatomic molecules (molecules made of pairs of atoms).
States and colours of halogens
Colours and States of Halogens
At room temperature, the following three halogens have these properties:
Chlorine
Colour: pale green.State: gas.
Iodine
Colour: dark grey.State: solid.
Bromine
Colour: red-brown.State: liquid.
Test for Chlorine
Insert damp litmus paper into a test tube containing a gas.If the gas is chlorine, the litmus paper will bleach and change colour from red to white.
Reaction between metals and halogens
When a metal atom transfers its outerelectronto a halogen, asaltis formed.
e.g. 2Na + Cl2→ 2NaCl
Noble gas (Group 0) uses
Noble gases can be used in light bulbs because they will NOT react with the hot metal filament.
Noble gas reactivity
Because noble gases are unreactive, they exist as single atoms (monatomic) instead of forming molecules.
Noble gas boiling points
The noble gases have low boiling points.But their boiling points do increase as you move down the periodic table. This is because the relative atomic mass increases lower down the periodic table.
Noble gas density and uses
The noble gases (in group 0) have low densities.Their densities do increase as you move down the periodic table because of their increasing relative atomic mass.This low density makes them useful in balloons.
Reaction between a halogen and a metal
metal + halogen → metal halide
Chlorine example
(EXAMPLE) Sodium + chlorine → sodium chloride2Na(s)+ Cl2(g)→ 2NaCl(s)
Metal halides properties
Ionic compounds that are solid at room temp
What are hydrogen halides ?
Halogens react with hydrogen to form hydrogen halides. Hydrogen halides are covalent compounds.
What type of solutions do hydrogen halides form when reacting with water ?
Acidic solutions
The hydrogen halides dissolve in water to form acidic solutions, such as hydrofluoric acid, hydrobromic acids and hydroiodic acid.Hydrogen chloride dissolves in water to form hydrochloric acid.The solutions produce H+ions, which make them acidic.
Chlorine example
Hydrogen + chlorine → hydrogen chlorideH2(g)+ Cl2(g)→ 2HCl(g)
What does hydrogen chloride form when it dissolves in water?
Hydrochloric acid
Define a spectator ion ?
Aspectatorion is an ion that doesn’t change during a chemical reaction.
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Displacement as redox reactions
Halogens
More reactive halogen
Each atom gains an electron
Reduced
Less reactive halogen
Each ion loses an electron
Oxidised
Explain why reactivity decreases down group 7
The difference in the atoms
-Going down the group, atoms getbigger.
-Theouterelectrons are, therefore, further from thenucleus.
-This means the attraction between thenegativelycharged electrons and thepositivelycharged nucleus arelessstrong.
2
The difference in reactivity
-Group 7 elements react to become ions with a1-charge. This means they gain1electron.
-Down the group, there islessattraction for the outer electrons. This means that the elements gain electronslesseasily.
Question 1
A scientist conducts 2 experiments.
Experiment ACl2(g)is bubbled through a solution of NaBr. An orange colour develops as bromine is produced.Experiment BBr2(g)is bubbled through a solution of NaCl. No observations are made.
Explain the observations or lack of observations. Write equations for any reactions that occur.
1
Describe experiment A
Chlorinedisplaces thebromideions in NaBr. This leads to the formation ofbrominewhich is orange.
Cl2+2NaBr →Br2+ 2NaCl
2
Describe experiment B
There are no observations is experiment B becausebrominecannot displace thechlorideions in NaCl.
3
Explain the results
This is becausereactivitydecreasesdowngroup7. Bromine is lower down thanchlorineand is, therefore, less reactive and cannot displace.
Why is sodium more reactive than lithium ?
Elements are more reactive if they can give awayelectronseasier to achieve anoblegasconfiguration.
2
Sodium’s outer electron is less strongly attracted to thepositivelycharged nucleus.
3
This is because the outer electron is agreaterdistance from the positive charge of the atom’s nucleus.
Why are group 1 elements very reactive ?
Electrons fill an atom’s shells in order of increasing energy.
The closer a shell is to the nucleus, the lower its energy level, so the first shell that is filled is the closest to the nucleus.
Why does more shells mean more reactive ?
More shells shields the electron from the nuclear charge of the nucleus, meaning a weaker attraction.
